This study is designed to characterize the central actions of drugs on intestinal motility and intestinal propulsion. All studies will be performed on intact unanesthetized animals. Studies of intestinal motility will be performed on cats surgically implanted with extracellular electrodes or extraluminal strain gage transducers at several loci along the small intestine. Suspected central and peripheral emetic agents will be administered either systemically or into a lateral cerebral ventricle of the brain. Emetic effectivenesss will be assessed for each agent and for each route of administration. Intestinal motor responses during emesis will be characterized for each agent. Drug and/or nerve transection experiments will determine the efferent nerve pathways responsible for the intestinal emetic response. Central and/or peripheral effects of drugs which produce diarrhea or constipation will be tested in rats surgically implanted with duodenal and intracerebroventricular cannulas. Intestinal propulsion will be determined by measuring the progression through the small intestine of an intraduodenally administered radioactive marker. Effects of drug agonists, receptor blocking agents and neurotransmitter synthesis inhibitors on intestinal transit, or their effects on other agents will be tested after central or peripheral administration. The results will increase our understanding of drugs which affect intestinal function therapeutically or as a side-effect and improve our knowledge of the central nervous system control of intestinal motility.